The most prominent character is the woman who is made to stay in the room with the yellow wallpaper. She is the focus as we see the story unfold through her eyes. Her husband is also key. He is controlling and his decisions regarding his wife's treatment are what drive the story. There may be other minor characters like the servants in the house, but they are not as central as the husband and wife.
The main character is the unnamed female narrator. She is a woman who is suffering from some sort of mental or nervous condition and is placed in a room with yellow wallpaper by her husband, who is also an important character. He is a doctor and believes that rest and isolation will cure his wife, but his actions actually lead to her further descent into madness.